In the conventional ink jet recording system, ink emerges from one or more exit orifices of a nozzle array which is connected to a source of high pressure fluid. The ink jet is then caused to be broken up into a stream of synchronized drops by the application of a periodic perturbation at the nozzle caused by an electromechanical transducer or a voltage applied to a synchronization electrode associated with the exit orifice. The synchronization electrode establishes an electric field which electrohydrodynamically perturbs the jet stream emerging from the jet nozzle structure. A charge electrode is positioned near the point of drop formation so that when a voltage is supplied to the charge electrode, a charge is drawn out to the tip of the jet. As the drop breaks off from the jet, it carries with it a charge proportional to the voltage applied to the charge electrode. The drops then leave the area of the charge electrode and pass through deflection plates onto a target paper or a catcher or gutter, depending upon whether the drops at this stage are charged or uncharged.
Nozzles for ink jet recorders take on a variety of forms and a number of processes are known for making them. For example, U.S. Pat. No. 3,921,916, which issued to Ernest Bassous on Nov. 25, 1975, discloses a process for fabricating membrane-type silicon nozzles. As indicated there, the nozzles are formed in crystallographically oriented monocrystalline silicon or similar material using anisotropic etching. U.S. Pat. No. 3,958,255, which issued to Charles Chiou et al on May 18, 1976 there is disclosed a novel nozzle structure and method for its fabrication using single crystal material oriented with the (100) planes parallel to the surface.
The challenge of accomplishing integrated or monolithic units in ink jet recorders has been met in various ways. Thus, in pending application Ser. No. 591,982, filed June 30, 1975, to G. J. Fan, et al, a magnetic transducer driven by a transformer is physically placed on the nozzle substrate. In U.S. Pat. No. 3,949,410, which issued to Ernest Bassous et al on Apr. 6, 1976, et al, the exit aperture of the nozzle opens into a slot whose walls form the synchronizing electrode structure.
However, in these and other well known nozzle configurations, the nozzle structure is distinct and apart from the charge electrode. For example, in pending application Ser. No. 543600, filed Jan. 23, 1975, to Ernest Bassous, et al, the charge electrode structure is spaced from the nozzle mounting plate by means of spacers.
The importance of the charge electrode in an ink jet recording apparatus has been recognized and some contributions have already been made to its improvement. Thus, in U.S. Pat. No. 3,984,843, which issued to Lawrence Kuhn on Oct. 5, 1976, charge electrodes are formed by a diffusion into an array of passages in a semiconductor substrate. Each diffusion may be connected to a charging circuit comprising a latch circuit and a shift register, which can be formed in the front surface of the substrate.
Also, numerous anisotropic etchants are known for monocrystalline silicon which include alkaline liquids or mixtures thereof. These include aqueous sodium hydroxide, aqueous potassium hydroxide, aqueous hydrazine, tetramethyl ammonium hydroxide, mixtures of phenols and amines such as a mixture of pyrocatechol and ethylene diamine with water, and a mixture of potassium hydroxide, n-propanol and water. These and other preferential etchants for monocrystalline silicon are usable in the process of the present invention for forming the charge electrode.
As is known, in anisotropic etching, crystalline materials are attacked at different rates in different crystallographic directions. With respect to the three most common low index crystal planes in monocrystalline silicon, the etch rate is greatest for (100) oriented silicon, somewhat less for (110) oriented silicon and is least for (111) oriented silicon. The preferred embodiment of the present invention uses single crystal silicon of (110) orientation. For further information on etching technology suitable for carrying out this invention, reference may be made to U.S. Pat. No. 3,770,533, which issued on Nov. 6, 1973, and to the article in the Journal of Electrochemical Society, 1965, Vol. 114, page 1965 et seq.
The present invention differs over the prior art in that charge electrodes and associated drive circuitry are formed in a monocrystalline silicon of (110) orientation. Although silicon substrates of other orientations, e.g., (100), may be used, (110) oriented silicon is preferred since it results in a greater packing density, more efficient charging and reduced crosstalk for an array of charge electrodes. The inventive process also permits the fabrication of the charge electrodes in the same silicon substrate in which the ink jet nozzle and its associated synchronization electrode are fabricated. The use of the present process requires no photolithograhic steps after the charge electrode aperture is formed by anisotropic etching. This provides an important advantage over other processes, since adequate photolithography cannot be performed after the apertures are fabricated.